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discopop_profiler

Call clang++ with DiscoPoP LLVM passes.

The DiscoPoP profiler consists of multiple LLVM libraries (CUGeneration, DPInstrumentation and DPReduction) to be passed to clang++ at compilation, as well as a runtime library for the instrumented code.

discopop_profiler wraps clang++ invocations to include the necessary compiler and linker flags to make use of the DiscoPoP features. To use one of the DiscoPoP passes, discopop_profiler is used instead of clang++, with one of the option flags --CUGeneration, --DPInstrumentation or --DPReduction to select the LLVM pass.

Pre-requisites

discopop_profiler is included in the PyPI package discopop. As such, it is installed with

pip install discopop

It is required that the DiscoPoP profiler is installed (see DiscoPoP profiler installation) and the environment variable DISCOPOP_INSTALL is set to the path where DiscoPoP is installed.

export DISCOPOP_INSTALL=<PATH_TO_LLVM_BUILD_FOLDER>

Usage

usage: discopop_profiler [--verbose] [--clang CLANG]
                         (--CUGeneration | --DPInstrumentation | --DPReduction)
                         <clang++ arguments>

Call clang++ with DiscoPoP LLVM passes.

optional arguments:
  -h, --help            Show this help message and exit.
  -V, --version         Show version number and exit.
  -v, --verbose         Show additional information such as clang++
                        invocations.
  --clang CLANG         Path to clang++ executable.
  --CUGeneration, --cugeneration
                        Obtain the computational unit (CU) graph of the target
                        application.
  --DPInstrumentation, --dpinstrumentation
                        Instrument the target application to obtain data
                        dependences.
  --DPReduction, --dpreduction
                        Instrument the target application to obtain the list
                        of reduction operations.

CU generation

To obtain the computational unit (CU) graph of the target application, please run the following command.

discopop_profiler --CUGeneration -c <C_File>

Dependence profiling

To obtain data dependences, we need to instrument the target application. Running the instrumented application will result in a text file containing all the dependences that are located in the present working directory.

discopop_profiler --DPInstrumentation -c <C_File> -o out.o
discopop_profiler --DPInstrumentation out.o -o <APP_NAME>
./<APP_NAME>

Identifying reduction operations

To obtain the list of reduction operations in the target application, we need to instrument the target application. Running the instrumented application will result in a text file containing all the reductions that are located in the present working directory.

discopop_profiler --DPReduction -c <C_File> -o out.o
discopop_profiler --DPReduction out.o -o <APP_NAME>
./<APP_NAME>

Usage with projects that use the CMake build system

Since discopop_profiler is invoked like a regular compiler, it is easy to run DiscoPoP instrumentation on projects that use a build system such as CMake.

  1. Configure CMake to use discopop_profiler as CMAKE_CXX_COMPILER: 
    cmake -DCMAKE_CXX_COMPILER="discopop_profiler" -DCMAKE_CXX_FLAGS="--DPInstrumentation" .
  2. Build the project with DiscoPoP instrumentation applied on the code: 
    make

Troubleshooting

clang++ executable not found in PATH

discopop_profiler expects to find clang++-8 or clang++ in your system's PATH. If clang is installed elsewhere, either add the installation location to your PATH, or set the location to the clang++ binary to be invoked with

discopop_profiler --clang=<PATH_TO_CLANG++_EXECUTABLE> ...

Compiler invocation

discopop_profiler prints the exact flags passed to clang++ if the --verbose flag is set.

discopop_profiler --verbose ...